The condition of nerve root signature or nerve root sign is poorly described in the horse literature. However there is a growing awareness of a syndrome affecting the forelimbs caused by compression of the nerve roots as they exit the spinal in the cervical vertebrae. The condition is very well described in humans and is now well described in dogs.
In the figure below, taken from Getty: Sisson and Grossman’s The Anatomy of Domestic Animals illustrates a cross section of a vertebrae, spinal cord and paired spinal nerves. The spinal nerves are arranged in pairs and each nerve connects to the spinal cord by a dorsal and ventral root. The dorsal root is the larger of the two and its fibres converge laterally to form a compact bundle, an enlargement known as the dorsal root ganglion. Moving further away from the ganglion the dorsal root joins up with the ventral root to form the spinal nerve. There is no ganglion in the ventral roots.
The dorsal root is usually sensory (afferent) whereas the ventral root is motor (efferent). The spinal nerves also carry fibres of the sympathetic nervous system, supplying glands and smooth muscle. The ganglia in the cervical and thoracic spine are outside to the dura mater and situated in the lateral vertebral or intervertebral foramina.
There are eight cervical spinal nerve pairs in the horse. They exit beneath the articular process joints through the intervertebral foramina. Degenerative joint disease involving the articular process joints can cause dorsal lateral compression of the spinal cord, resulting in ‘long tract’ signs of ataxia and paresis. This is reviewed in the section of Cervical Stenotic Myelopathy under type II CSM.
An enlarged APJ can also put pressure onto the nerve roots and spinal nerves after they have exited the spinal cord. The can result in a neurologic lameness in one or both forelimbs. This condition is also known medically as cervical radiculopathy. The diagnosis can be very difficult to make. Certainly imaging is important with both plain radiography and ultrasound both useful tools to demonstrate enlargement and distortion of the APJs. CT imaging is ideal.
The treatment is to medicate the APJs (intraarticular injection) and/or around the nerve roots (perineural injection) under ultrasound guidance with cortisone.
Tags: Neurological Diseases